The present invention relates to a process for producing methionine by a hydrolysis reaction of 5-[(2-(methylthio)ethyl)]imidazolidine-2,4-dione [see the reaction scheme (1) shown below].
                Methionine is useful as an additive for animal feed.        
As an example of known processes for producing methionine, there is a process which comprises hydrolysis of 5-[(2-methylthio)ethyl]imidazolidine-2,4-dione under a basic condition using a basic potassium compound such as potassium carbonate or potassium hydrogen carbonate. According to this process, methionine can be separated and obtained as a crystal by introducing carbon dioxide into a reaction solution after hydrolysis to induce crystallization.
An example of the above-described methionine producing process which comprises carrying out hydrolysis in a stirred continuous reaction tank is disclosed (e.g., JP-A 2007-99778).
It is also known that a crystal of methionine is usually difficult to stabilize because it is a flake crystal, and therefore a flocculant is required for crystallization.
When hydrolysis is carried out in a stirred continuous reaction tank as described above, the resultant methionine crystal has a low bulk density, resulting in a high equipment cost.